code-utils/imgproxy.go

package main

// imgproxy.go：远程图片拉取。
// WebView 页面源是 http://wails.localhost，直接加载外站 HTTPS 图常会破图。
// 优先经 Go 拉成 dataURL（FetchRemoteImageAsDataURL）；AssetServer /__ccimg 作兜底。

import (
	"context"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"sync"
	"time"
)

const (
	imgProxyPath     = "/__ccimg"
	imgProxyMaxBytes = 12 << 20 // 12MB
)

var imgProxyClient = &http.Client{Timeout: 20 * time.Second}

var (
	imgDataURLMu    sync.Mutex
	imgDataURLCache = map[string]string{}
	errBadImageURL  = errors.New("bad url")
)

// remoteImageMiddleware 拦截 /__ccimg?u=<urlencoded http(s) URL>，拉取上游图片并回传。
func remoteImageMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		path := strings.TrimSuffix(r.URL.Path, "/")
		if path != imgProxyPath {
			next.ServeHTTP(w, r)
			return
		}
		raw := strings.TrimSpace(r.URL.Query().Get("u"))
		data, ct, err := fetchRemoteImage(r.Context(), raw)
		if err != nil {
			code := http.StatusBadGateway
			if errors.Is(err, errBadImageURL) {
				code = http.StatusBadRequest
			}
			http.Error(w, err.Error(), code)
			return
		}
		w.Header().Set("Content-Type", ct)
		w.Header().Set("Cache-Control", "private, max-age=86400")
		_, _ = w.Write(data)
	})
}

func fetchRemoteImage(ctx context.Context, raw string) ([]byte, string, error) {
	raw = strings.TrimSpace(raw)
	u, err := url.Parse(raw)
	if err != nil || u.Host == "" || (u.Scheme != "http" && u.Scheme != "https") {
		return nil, "", errBadImageURL
	}
	if ctx == nil {
		ctx = context.Background()
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return nil, "", errBadImageURL
	}
	req.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36")
	req.Header.Set("Accept", "image/avif,image/webp,image/apng,image/*,*/*;q=0.8")
	resp, err := imgProxyClient.Do(req)
	if err != nil {
		return nil, "", errors.New("upstream unreachable")
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, "", errors.New("upstream error")
	}
	ct := resp.Header.Get("Content-Type")
	if i := strings.Index(ct, ";"); i >= 0 {
		ct = strings.TrimSpace(ct[:i])
	}
	data, err := io.ReadAll(io.LimitReader(resp.Body, imgProxyMaxBytes+1))
	if err != nil {
		return nil, "", errors.New("upstream read failed")
	}
	if len(data) > imgProxyMaxBytes {
		return nil, "", errors.New("image too large")
	}
	if len(data) == 0 {
		return nil, "", errors.New("empty image")
	}
	if ct == "" || (!strings.HasPrefix(ct, "image/") && !strings.Contains(ct, "octet-stream")) {
		if sniffed := sniffImageMIME(data); sniffed != "" {
			ct = sniffed
		}
	}
	if ct == "" {
		ct = "application/octet-stream"
	}
	return data, ct, nil
}

func sniffImageMIME(b []byte) string {
	if len(b) >= 3 && b[0] == 0xff && b[1] == 0xd8 && b[2] == 0xff {
		return "image/jpeg"
	}
	if len(b) >= 8 && string(b[:8]) == "\x89PNG\r\n\x1a\n" {
		return "image/png"
	}
	if len(b) >= 6 && (string(b[:6]) == "GIF87a" || string(b[:6]) == "GIF89a") {
		return "image/gif"
	}
	if len(b) >= 12 && string(b[:4]) == "RIFF" && string(b[8:12]) == "WEBP" {
		return "image/webp"
	}
	return ""
}

// FetchRemoteImageAsDataURL 由 Go 拉取远程图片并返回 dataURL，绕过 WebView 外站限制。
func (a *App) FetchRemoteImageAsDataURL(rawURL string) (string, error) {
	rawURL = strings.TrimSpace(rawURL)
	if rawURL == "" {
		return "", errors.New("EMPTY_URL")
	}
	if strings.HasPrefix(rawURL, "data:") {
		return rawURL, nil
	}
	imgDataURLMu.Lock()
	if cached, ok := imgDataURLCache[rawURL]; ok {
		imgDataURLMu.Unlock()
		return cached, nil
	}
	imgDataURLMu.Unlock()

	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
	defer cancel()
	data, ct, err := fetchRemoteImage(ctx, rawURL)
	if err != nil {
		return "", err
	}
	if !strings.HasPrefix(ct, "image/") {
		ct = "image/png"
		if sniffed := sniffImageMIME(data); sniffed != "" {
			ct = sniffed
		}
	}
	out := fmt.Sprintf("data:%s;base64,%s", ct, base64.StdEncoding.EncodeToString(data))
	imgDataURLMu.Lock()
	if len(imgDataURLCache) > 128 {
		imgDataURLCache = map[string]string{}
	}
	imgDataURLCache[rawURL] = out
	imgDataURLMu.Unlock()
	return out, nil
}